A CT (computerised tomography) scanner is a special kind of X-ray machine. Instead of sending out a single X-ray through your body as with ordinary X-rays, several beams are sent simultaneously from different angles.

2.How does a CT scanner work?

The X-rays from the beams are detected after they have passed through the body and their strength is measured.Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have passed through denser tissue such as bone will be weaker.A computer can use this information to work out the relative density of the tissues examined. Each set of measurements made by the scanner is, in effect, a cross-section through the body.The computer processes the results, displaying them as a two-dimensional picture shown on a monitor.

3.What are CT scans used for?

CT scans are far more detailed than ordinary X-rays. The information from the two-dimensional computer images can be reconstructed to produce three-dimensional images by some modern CT scanners. They can be used to produce virtual images that show what a surgeon would see during an operation.CT scans have already allowed doctors to inspect the inside of the body without having to operate or perform unpleasant examinations. CT scanning has also proven invaluable in pinpointing tumours and planning treatment with radiotherapy.

4.What is the CT scanner used for?

The CT scanner was originally designed to take pictures of the brain. Now it is much more advanced and is used for taking pictures of virtually any part of the body.The scanner is particularly good at testing for bleeding in the brain, for aneurysms (when the wall of an artery swells up), brain tumours and brain damage. It can also find tumours and abscesses throughout the body and is used to assess types of lung disease.In addition, the CT scanner is used to look at internal injuries such as a torn kidney, spleen or liver; or bony injury, particularly in the spine. CT scanning can also be used to guide biopsies and therapeutic pain relieving procedures.

5.How is a CT scan prepared for?

If the patient is receiving an abdomen scan, for example, they will be asked not to eat for six hours before the test. They will be given a drink containing gastrografin, an aniseed flavoured X-ray dye, 45 minutes before the procedure. This makes the intestines easier to see on the pictures.Sometimes a liquid X-ray dye is injected into the veins during the test.This also makes it easier to see the organs, blood vessels or, for example, a tumour. The injection might be a little uncomfortable, and some people also experience a feeling of warmth in their arm.

6.How is a CT scan carried out?

The scanner looks like a large doughnut.During the scan the patient lies on a bed, with the body part under examination placed in the round tunnel or opening of the scanner.The bed then moves slowly backwards and forwards to allow the scanner to take pictures of the body, although it does not touch the patient.The length of the test depends on the number of pictures and the different angles taken.

7.Does a CT scan hurt?

The examination does not hurt but some people find it uncomfortable to lie in the tunnel.As there is little room inside the tunnel, people who suffer from severe claustrophobia sometimes have problems with CT scans.Let the doctors and radiographers know if this might be a problem. Other people get slightly nervous because of the whirring noise the machine makes while working.

8.Is a CT scan dangerous?

Far more X-rays are involved in a CT scan than in ordinary X-rays, so doctors do not recommend CT scans without a good medical reason.Some patients may experience side effects due to allergic reactions to the liquid dye injected into the veins.In very rare cases, this dye has been known to damage already weakened kidneys. It is important to let the X-ray doctors or technicians know if you have any allergies, asthma or kidney trouble, prior to having the X-ray dye injected.

9.How is a CT scan read?

A CT scan can give the doctor a much clearer picture of the inside of the body than an ordinary X-ray. For example, different types of tissue such as bone, muscle and fatty tissue are easy to see on a CT scan. When looking at the abdomen, the scan shows various organs such as the pancreas, spleen and liver.When it is necessary to look at the brain, the areas containing liquid – the ventricles – are also clearly defined.Very small shadows on the lungs can also be detected using CT and there are now studies looking into using it as a screening test for lung.

10.Can I take my medicine before a CT scan?

Yes, please take medicines before the CT scan, with the exception of diabetic medicines.Consult your physician before the test for instructions.

11.How long will it take to do a CT scan?

The exam will last no longer than an hour, depending on the preparation needed and whether it includes the use of a contrast medium.The scan itself may take less than a minute on the newest machines.Most scans take just a few minutes to complete.

12.Will the radiation that I receive from the CT scan hurt me?

CT scans are similar to those of conventional X-rays. During the CT scan, you’re briefly exposed to radiation. But doctors and other scientists believe that CT scans provide enough valuable information to outweigh the associated risks.

13.What will I experience during and after the procedure?

During the CT scan, you lie on a narrow table that slides through the opening of the gantry. You may lie on your back, side or stomach, depending on the area to be scanned. The table can be raised or lowered. Straps and pillows may help you stay in position. During a CT scan of the head, the table may be fitted with a special cradle that holds your head still. CT scans are painless. If your exam involves use of an intravenous contrast medium, you may feel a brief sensation of heat or experience a metallic taste in your mouth. If you receive the contrast medium through an enema — to help highlight your lower gastrointestinal region — you may feel a sense of fullness or cramping. After the exam you can return to your normal routine. If you were given a contrast medium, your doctor, a nurse or the CT technologist performing the scan may give you special instructions. You may be asked to wait for a short time in the radiology department to ensure that you feel well after the exam. After the scan, you'll likely be told to drink lots of fluids to help your kidneys remove the medium from your body.

14.Will I have to take a CT contrast or dye, and can I be allergic to it?

It depends on which part of your body is being scanned. Although rare, the contrast medium Involved in a CT scan poses a slight risk of allergic reaction. Most reactions are mild and result in hives or itchiness.For people with asthma who become allergic to the contrast medium, the reaction can be an asthma attack.In rare instances, an allergic reaction can be serious and potentially life-threatening — including swelling in your throat or other areas of your body. If you experience hives, itchiness or swelling in your throat during or after your CT exam, immediately tell your technologist or doctor.If you've had a reaction to a contrast medium in the past, and you need a diagnostic test that may require a contrast medium again, talk to your doctor. Be sure to let your doctor know if you have kidney problems, since contrast material that's injected into a vein is removed from your body by your kidneys and could potentially cause further damage to your kidneys.If you have had a prior reaction to contrast media or have asthma or allergies, there's an increased risk of a reaction to the contrast medium. Diabetes, asthma, heart disease, kidney problems or certain thyroid conditions may increase your risk of a reaction to contrast media.

15.Will I need someone to drive for me after the CT scan?

No, the CT scan is a safe test that will not affect your ability to drive.

16.How and when will I get my results?

CT images are stored as electronic data files and usually reviewed on a computer. A radiologist interprets these images and sends a report to your doctor.

17.What is Children's CT?

CT scanning—sometimes called CAT scanning—is a noninvasive medical test that helps physicians diagnose and treat medical conditions.CT scanning combines special x-ray equipment with sophisticated computers to produce multiple images or pictures of the inside of the body. These cross-sectional images of the area being studied can then be examined on a computer monitor, printed or transferred to a CD.CT scans of internal organs, bones, soft tissue and blood vessels provide greater clarity and reveal more details than regular x-ray exams.Newborns, infants and older children may undergo CT scanning.

18.What are some common uses of the procedure?

Physicians can use the CT examination to help detect a wide range of abnormalities, including those from injury or illness, in almost any part of a child's body.In children, CT is typically used to diagnose causes of abdominal pain, evaluate for injury after trauma, diagnose and stage cancer, monitor response to treatment for cancer, and diagnose and monitor infectious or inflammatory disorders.CT may also be performed to evaluate blood vessels throughout the body. With CT, it is possible to obtain very detailed pictures of the heart and large blood vessels in children, even newborn infants.

19.What does the equipment look like?

The CT scanner is typically a large machine with a hole, or short tunnel, in the center. A moveable examination table slides into and out of this tunnel. In the center of the machine, the x-ray tube and electronic x-ray detectors are located opposite each other on a ring, called a gantry, which rotates around the patient. The computer that processes the imaging information and monitor are located in a separate room where the CT technologist sits. The technologist will always be able to see your child in the CT scanner.

20.What are the limitations of Children's CT?

A person who is very large may not fit into the opening of a conventional CT scanner or may be over the weight limit—usually 450 pounds—for the moving table.Other imaging methods such as ultrasound or magnetic resonance (MR) imaging can provide pictures of certain areas of the body that sometimes are as good as or better than those obtained by CT scanning. Working together, your primary care physician or pediatrician and the radiologist will decide which type of examination is best for your child.